I guess there were no way for her to know her husband was alive or not, a real Schrödinger’s spouse situation.
And just to hammer it home that infidelity is wrong, I’m surprised the studio didn’t go with an ending where Bogart got hit by that German and covered up that he was bleeding with that big trench coat, only to collapse after the plane had taken off. But I guess since it was a war movie it was bad for morale to have the “good guy” die.